1. Field of the Invention
The present invention relates to a printer to print on a printing medium which has been fed, especially relates to controlling a drive current to feed the printing medium.
2. Description of Related Art
Conventionally, there has been widely used a printer which is arranged to operate predetermined printing on a printing medium with a line thermal head, while the printer feeds the printing medium by a printing medium feeding part of a platen. The printing medium may include rolled printing mediums of various widths for thermal printing, each of which is directly mountable in the printer, and a rolled printing medium with a thermal ink ribbon set in a dedicated holder.
A drive current to drive the platen has been generally set high, considering the various widths of the printing mediums to be used. Accordingly, the drive current to drive the platen becomes excessive depending on the widths of the printing mediums. This would cause problems in printing quality and wasteful power consumption.
Japanese unexamined patent publication No. H11(1999)-100017 discloses a label printer having the following structure. This label printer determines the width and a feeding speed of a label sheet based on format data included in print data imported from a personal computer through a communication I/F. In case the label printer determines, e.g., the label sheet is narrow, the printer controls and reduce the amount of electrical power to be supplied to a DC motor, considering that a frictional force of the label sheet between a platen and a line thermal head becomes smaller as the label sheet is narrower and the feeding speed of the label sheet is faster.
However, the label printer in the '017 publication, as above, determines the width and the feeding speed of the printing medium based on the format data included in the print data imported from the personal computer through the communication I/F. The printer does not detect directly the printing medium itself. Therefore, the printer can hardly find that a printing medium of wrong width is being set. Further, even when the width is correct, the printer cannot distinguish materials of the printing mediums.
Furthermore, following points can be pointed out, considering that the frictional force of the label sheet between the platen and the line thermal head becomes smaller as the label sheet is narrower and the feeding speed of the label sheet is faster. Both widths of the thermal ink ribbon and the thermal head are equal in order not to contact the platen with the line thermal head directly. That is, the width of the thermal ink ribbon does not vary with the width of the printing medium. This results in that a frictional resistance increases because the contacting area of the platen and the line thermal head becomes larger as the width of the printing medium is narrower, when thermal paper of different width or a pair of the printing medium and the thermal ink ribbon having the same width as the printing medium to reduce costs is used. This provides an inverse result in the above '017 publication in view of the width of the thermal ink ribbon.